In a conventional image forming device, as disclosed in Japanese Patent Application-Publication No. HEI-5-270091, a carriage with a recording head mounted thereon is generally supported slidably by a cylindrical guide shaft so that the carriage can reciprocate in a main scanning direction.
Since the carriage supported by the cylindrical guide shaft has excellent dimensional accuracy and high rigidity, fluctuation in a so-called paper gap between a nozzle surface of the recording head and a recording medium can be reduced, and thus a high-quality recorded image is easily obtained. However, a frame structure as well as the cylindrical guide shaft are expensive. Also, in order to detach the carriage from the guide shaft for maintenance and replacement operations, it is necessary to first detach the guide shaft from the frame, and then the carriage is detached from the guide shaft. In order to attach the carriage to the guide shaft, the reverse procedure must be performed, thereby posing considerable difficulty in attachment and detachment of the carriage.
U.S. Pat. No. 6,789,966 and US2005/0243125 disclose printers having following structures. That is, a plate-like first guide member is disposed on an upstream side of a plate-like second guide member with respect to a sheet feeding direction, with a board-like platen interposed therebetween. Both the first and second guide members extend in a main scanning direction perpendicular to the sheet feeding direction. A recording head is provided on the lower surface of a carriage that is slidably supported by the first and second guide members. The carriage is connected to a part of an endless belt extending in the main scanning direction and driven by a carriage driving motor to reciprocate.
Guide parts (sliding protrusions) which contact (slide over) the upper surfaces as sliding surfaces of the first and second guide members are provided on the lower surface of the carriage, thereby controlling a printing gap (paper gap) between the recording head on the carriage and a sheet on the platen. A carriage guide plate is formed at the second guide member (guide member that is closer to a place coupled to the endless belt), by means of cutting and pulling up the cut portion. In this manner, the carriage is controlled not to rotate around a vertical axis when the carriage moves by being pulled by the endless belt.
In U.S. Pat. No. 6,789,966, the carriage mounts an ink cartridge thereon. On the other hand, in US2005/0243125, an ink cartridge is placed to be stationary in a main housing of a printer, and the ink cartridge is coupled to the carriage through an ink supply tube.
In the printer disclosed in US2005/0243125, a driving pulley is fixedly attached to a carriage motor (CR motor) fixed at one end of a frame of the main housing or the second guide member in the main scanning direction, and a driven pulley is freely rotatably attached to the other end thereof in the main scanning direction. Flange parts are formed to the driving pulley and the driven pulley so that the endless belt wound thereon does not get off in the axis direction of the pulleys. The position of a part of the endless belt that is attached to the carriage is set higher in the vertical direction than the positions where the endless belt is wound around the pulleys, so that the carriage is pressed against the upper surface of the second guide member due to a downward component force of a tensile force exerted on the endless belt. In other words, it is possible to eliminate unstability, for example, the possibility that the carriage floats up from the second guide member when the carriage is pulled by the endless belt.
With the configuration disclosed by U.S. Pat. No. 6,789,966 and US2005/0243125, the part of the endless belt that is coupled to the carriage is located above the guide part of the carriage which contacts the upper horizontal sliding surface of the second guide member or downstream of the guide part that is on the downstream side of the first guide member. Thus, when the downward component force of the tensile force exerted on the endless belt is applied at a belt-coupling position of the carriage where the carriage is coupled to the endless belt, the guide parts of the carriage float up from the sliding surface of the first guide member on the side further from the belt-coupling position. That is, the carriage is subjected to a moment for rotating around an axis parallel to the main scanning direction. Accordingly, the orientation of the carriage during an image forming operations becomes unstable, and thus the accuracy of the paper gap also becomes degraded. As a result, quality of a recorded image is deteriorated or becomes unstable.